The present invention relates to a static gas turbine component comprising an inner and an outer annular support member and a plurality of circumferentially spaced radial struts arranged between said support members for transmitting structural loads. The invention also relates to a method for repairing the static gas turbine component.
The gas turbine component may be used in stationary gas turbine engines, but is especially advantageous for aircraft jet engines. Jet engine is meant to include various types of engines, which admit air at relatively low velocity, heat it by combustion and shoot it out at a much higher velocity. Accommodated within the term jet engine are, for example, turbojet engines and turbo-fan engines. The invention will below be described for a turbo-fan engine, but may of course also be used for other engine types.
An aircraft gas turbine engine of the turbofan type generally comprises a forward fan and booster compressor, a middle core engine, and an aft low pressure power turbine. The core engine comprises a high pressure compressor, a combustor and a high pressure turbine in a serial relationship. The high pressure compressor and high pressure turbine of the core engine are interconnected by a high pressure shaft. The high-pressure compressor, turbine and shaft essentially form a high pressure rotor. The high-pressure compressor is rotatably driven to compress air entering the core engine to a relatively high pressure. This high pressure air is then mixed with fuel in the combustor and ignited to form a high energy gas stream. The gas stream flows aft and passes through the high-pressure turbine, rotatably driving it and the high pressure shaft which, in turn, rotatably drives the high pressure compressor.
The gas stream leaving the high pressure turbine is expanded through a second or low pressure turbine. The low pressure turbine rotatably drives the fan and booster compressor via a low pressure shaft, all of which form the low pressure rotor. The low pressure shaft extends through the high pressure rotor. Most of the thrust produced is generated by the fan. Engine frames are used to support and carry the bearings, which in turn, rotatably support the rotors. Conventional turbo fan engines have a fan frame, a mid-frame and an aft turbine frame.
The engine is mounted to the aircraft at a forwardly located fan frame forward mount on the fan frame and at a rearwardly located turbine frame aft mount on the turbine frame.
The structural strength of the gas turbine engine hinges upon a limited number of engine structures, also known as cases or housings. These structures therefore represent the skeleton of the engine. The structures are highly loaded during operation of the engine. The structures usually comprise a bearing house for the engine shafts, a gas flow channel in the form of an annular duct and radial struts which form the link between the inner and outer parts of the engine. Thus the air is forced rearwardly through the openings between adjacent struts. The inventive gas turbine component forms such a structure.
Aircraft engines should be as light as possible. In order to build as light engines as possible, the engine's non-rotating, load transmitting, structural parts should be as stiff and rigid as possible. One way of achieving this is to use composites due to the fact that they have a high specific stiffness and strength.
Aircraft engines must be able to work for different load cases and certain occurrences in order to operate safely. One specific problem is so-called Foreign Object Damage (FOD). One category of FOD's is when particles, birds or hail are sucked in through the engine intake and hit a strut (located either before or after the fan). If the strut is not arranged for transmitting loads during operation, deteriorated mechanical functionality may be accepted, but if the strut is arranged for transmitting loads during operation, it must either be sufficiently strong for enduring the operational loads with a deteriorated mechanical functionality or be repaired or exchanged.
Depending on the geometrical complexity and the risk for geometrically extended damages, it is difficult to make local repairs.
It is desirable to achieve a static gas turbine component comprising an inner annular support member, an outer annular support member and a plurality of circumferentially spaced radial struts arranged between said support members, with a design that creates conditions for easy repair when it has been damaged during use.
According to an aspect of the present invention, each of a plurality of said struts comprises a load carrying core rigidly fixed to both the inner and the outer support members forming a unitary carcass with the members, an impact resistant shell surrounding the core, and an energy absorbing material arranged between the core and the shell.
Thus, the carcass forms a unitary load transmitting structure. In the event of a foreign object colliding with a strut, the impact resistant shell is designed to withstand a smaller impact energy without being damaged. In the event of a larger impact energy, the shell will be severely damaged while the energy absorbing material will absorb a larger portion of the impact energy. In this way, the load transmitting core is protected even for large energy impacts. Thus, the carcass can be maintained intact during use.
The shell and the energy absorbing material are removably connected to the load transmitting carcass. Thus, when it is time for repair, the shell and the energy absorbing material are removed from the carcass, leaving the carcass homogeneous, ie in the form of one single piece. The shell is preferably removed mechanically, while the energy absorbing material may be removed mechanically or chemically.
A new impact resistant shell and a new energy absorbing material are thereafter applied to the cores of the used unitary carcass.
According to an aspect of the invention, the energy-absorbing material forms a continuous structure around the core. Thus, the energy-absorbing material completely surrounds the core in a cross section of the strut, forming a distance between the shell and the core around its complete circumference. In other words, the core is completely embedded in the energy-absorbing material.
According to an aspect of the invention, the energy absorbing material comprises a polymer composite. This creates conditions for a light, stiff and strong structure.
It is also desirable to achieve a time and/or cost efficient method for repairing the static gas turbine component.
According to an aspect of the present invention, after use of the component, the used impact resistant shell and the used energy absorbing material of each strut are removed from each core of the unitary carcass, and that a new impact resistant shell and a new energy absorbing material are applied to the cores of the used unitary carcass.
Further advantageous embodiments and further advantages of the invention emerge from the detailed description below.